@timbba: You are kind of hijacking this bug which not about your mentioned problem.
Despite that I am not able to reproduce it with my "simple" multimon-setup: latop + external-monitor (set as primary) with plank following the primary-monitor; connecting/disconnecting the external-monitor results in the expected behaviour: wingpanel+plank gets moved to the external-monitor on connect and moved back to the laptop on disconnect.
Please file a new bug for your issue and describe your actions and used settings.
@timbba: You are kind of hijacking this bug which not about your mentioned problem.
Despite that I am not able to reproduce it with my "simple" multimon-setup: latop + external-monitor (set as primary) with plank following the primary-monitor; connecting/ disconnecting the external-monitor results in the expected behaviour: wingpanel+plank gets moved to the external-monitor on connect and moved back to the laptop on disconnect.
Please file a new bug for your issue and describe your actions and used settings.